The present invention relates to a method for cooling and preservation of fish and for products made from fish treated according to said method. The method comprises cooling of the fish by means of a cooling medium in tanks, containers or other suitable facilities.
The problems with present technology in this field are the quality of the raw material delivered to factories etc. for further processing, both with regard to consistency and degradability due to enzymatic and bacterial activity.
It is generally known to cool down the fish raw material to temperatures of 0.degree. to -5.degree. C. in order to slow down the degrading bacterial activity. The fish might for instance be cooled down in tanks on board the ship by circulating sea water or fresh water. The main problem with using sea water is that the NaCl content of the raw material gets too high, thereby giving too high content of this salt in the fish meal. A further consequence of this is that the price the fisherman gets for the fish might decrease with increasing content of NaCl in the fish delivered.
Cooling of the raw material by means of ice or ice-slurry is also generally known. A special type of ice slurry is called binary ice which is a suspension of ice crystals in an aqueous solution. Cooling of for instance fish on board a trawler by means of binary ice will generally cool the fish much quicker than with chilled sea water only. Binary ice as a secondary refrigerant is further described in a paper by J Paul in the 19th International Congress of Refrigeration 1995. Proceedings, Volume IVb, pages 947-954.
Application of preservative agents is also generally known in the art. Thus it is known to add acetic acid or a mixture of acetic acid and about 15 weight % sulphuric acid. The application of acetic acids does, in spite of giving improved quality of the raw material, have several disadvantages. The acid is corrosive to the equipment and requires expensive high quality steel. Those working with this acid have to protect themselves against etching effects of the acid. Further, in order to attain preservative effect the pH should be about 6, but this might cause problems with this acidic agent, as pH&lt;6 could result in autolyses and give problems with the consistency of the fish raw material.
The above known technology is described in the following reports from "Norwegian Herring Oil and Meal Industry Research Institute" (SSF):
Reports from SSF No. 1, 1991, pages 17-20: "Longterm preservation of winter capelin" By Mr. Agnar Mjelde PA1 Reports from SSF No.2, 1990, pages 7-12: "Fresh watercooling of blue whiting" By Mr. Tor Larsen PA1 Reports from SSF No. 1, 1989, pages 4-8: "Preservation by acetic acid ready for practical use?" By Mr. Tor Larsen